fix(music-lab): cache-buster query 제거 + DALL·E prompt에 background_keyword 활용

1. video.py _container_to_nas, orchestrator.py _local_path에서 path 변환 전 ?쿼리 strip
   — 이전 commit 20c5268의 cache-buster ?v=...가 Windows path로 그대로 전달되어 input_validation 실패하던 문제 픽스
2. cover.py _generate_with_dalle가 background_keyword를 prompt에 포함
   — 사용자가 PipelineStartModal에서 '배경 키워드' 입력 시 처음부터 원하는 분위기 cover 생성

music-lab/app/pipeline/cover.py

@@ -94,7 +94,8 @@ async def generate(*, pipeline_id: int, genre: str, prompt_template: str,
     if api_key:
         try:
             await _generate_with_dalle(prompt_template, mood, feedback, out_path,
-                                       api_key=api_key, model=model)
+                                       api_key=api_key, model=model,
+                                       background_keyword=background_keyword)
         except (httpx.HTTPError, httpx.TimeoutException, KeyError, ValueError, OSError) as e:
             logger.warning("DALL·E 실패 — 폴백: %s", e)
             error = str(e)
@@ -114,8 +115,11 @@ async def generate(*, pipeline_id: int, genre: str, prompt_template: str,
 
 async def _generate_with_dalle(prompt_template: str, mood: str,
                                 feedback: str, out_path: str,
-                                *, api_key: str, model: str) -> None:
+                                *, api_key: str, model: str,
+                                background_keyword: str = "") -> None:
     prompt = prompt_template
+    if background_keyword:
+        prompt = f"{prompt}, {background_keyword}"  # 사용자 직접 지정 keyword 우선 적용
     if mood:
         prompt = f"{prompt}, {mood} mood"
     if feedback:

music-lab/app/pipeline/orchestrator.py

@@ -284,6 +284,8 @@ def _local_path(media_url: str) -> str:
     """
     if not media_url:
         return ""
+    # Strip query string (e.g., cache-buster ?v=...)
+    media_url = media_url.split("?", 1)[0]
     base_media = os.getenv("VIDEO_MEDIA_BASE", "/media/videos")
     base_data = os.getenv("VIDEO_DATA_DIR", "/app/data/videos")
     if media_url.startswith(base_media):

music-lab/app/pipeline/video.py

@@ -94,6 +94,10 @@ def _container_to_nas(container_path: str) -> str:
     """ /app/data/videos/3/cover.jpg → /volume1/docker/webpage/data/videos/3/cover.jpg
         /app/data/abc.mp3            → /volume1/docker/webpage/data/music/abc.mp3
     """
+    if not container_path:
+        return ""
+    # Strip query string (e.g., cache-buster ?v=...)
+    container_path = container_path.split("?", 1)[0]
     if container_path.startswith("/app/data/videos/"):
         return container_path.replace("/app/data/videos/", NAS_VIDEOS_ROOT + "/", 1)
     if container_path.startswith("/app/data/"):